I. Introduction
Simultaneous wireless information and power transfer (SWIPT) attracts more and more attention in the literature in recent years for the devices adopting the SWIPT technology can scavenge energy from the radio frequency (RF) to drive their operations [1]. In [2], the authors assumed that the receiver can collect energy as well as decoding information from the same RF signals at the same time, which does not hold in practice. In [3], two practical receiver architectures, named time switching relaying (TSR) and power splitting relaying (PSR) are proposed, and the former harvests energy and decoded information based on different time slots and the latter utilizes a power splitting (PS) factor to divide the received power into two portions for harvesting energy and decoding information, respectively.